The present invention relates to a slip control method for a clutch which is situated between the engine and the transmission of a motor vehicle and is regulated via a differential speed between the clutch input speed and the clutch output speed.
The clutch has a positioning drive which allows the clutch to be adjusted into a position defined by a position setpoint signal. For this purpose, the clutch input speed and the clutch output speed are detected via rotational speed sensors, and a position setpoint signal is generated as a function of the difference between these rotational speeds (slip speed) in such a way that the slip is equal to a predefined setpoint slip.
Control methods of this type and devices for carrying out such methods are known from the related art. Thus, German Patent Application No. 42 41 995 A1, related to U.S. Pat. No. 5,403,250 which is hereby incorporated by reference herein, discloses a method and a device for adjusting the clutch slip of a propulsion engine of a motor vehicle in the downstream friction clutch as viewed in the direction of the force flux. A control variable formed from a characteristics map for the setpoint value of the clutch slip as a function of the operating point of the propulsion engine is made to act directly on the clutch actuator which makes it possible to adjust the clutch slip.
EP 0 494 608 B1, related to U.S. Pat. No. 5,322,150 which is hereby incorporated by reference herein, also discloses a system and a method for regulating the slip of an automated friction clutch situated between the engine and the transmission of a motor vehicle. The system includes a positioning drive which adjusts the clutch, as a function of the position setpoint signal, into a position defined by the position setpoint signal. The system also includes sensors for the clutch input speed and the clutch output speed, and a slip control device which generates the position setpoint signal as a function of the instantaneous difference of the rotational speeds detected, in such a way that the instantaneous difference between the rotational speeds is equal to a predefined setpoint speed difference. This system is further characterized by the fact that the slip regulating device is associated with a clutch characteristics curve memory which stores a position setpoint signal in the form of a characteristics curve as a function of data which represents the torque transmitted by the clutch in its setpoint position. The clutch characteristics curve memory generates the position setpoint signal corresponding to the value of the instantaneous engine torque detected by a torque detection device. The slip regulating device superimposes this position setpoint signal of the clutch characteristics curve memory on a regulating component generated by its regulator to generate the position setpoint signal. Using this method and this device, it is possible to maintain the clutch slip with a high quality of control.
Furthermore, DE 36 24 755 A1, related to British Patent Application No. 2197049 which is hereby incorporated by reference herein, describes a method for reducing torsional vibrations in the power train of a motor vehicle and for diminishing the noise caused thereby. The friction clutch situated between the engine and the transmission is controlled by a slip regulating circuit whose setpoint value generator controls the slip as a function of the structure-borne noise level. The maximum value of the slip is limited as a function of the engine speed, the maximum value decreasing to zero with increasing engine speed.
To isolate the power train of a vehicle from engine vibrations in vehicles having an automated clutch, in certain rotational speed ranges the clutch is operated at a low slip, as described previously. The isolation thus achieved considerably increases the ride comfort. However, the differential speed at the clutch must be adjusted relatively accurately for this purpose. An excessive slip results in increased power input and wear; excessively low slip may result in seizing of the clutch and thus in reduced ride comfort. Such a slip regulation generally assumes automated clutch actuation. According to the above-cited related art, such a slip regulation is implemented by modulating the clutch torque to be transmitted, i.e., via a control variable which acts upon the positioning drive of the clutch, opening or closing it to varying degrees. However, when such an intervention via a control variable takes place, the output torque of the clutch, i.e., the drive torque acting upon the vehicle, is modulated, which may feel unpleasant to the driver and diminishes the ride comfort.